A hot section of a turbine blade of a gas turbine has conventionally been cooled by the discharged air or bleed air of a compressor, but it is contrived to cool a stationary blade of a gas turbine by using steam in place of air as one means for improving the gas turbine efficiency.
In the steam cooling of the stationary blade of gas turbine, the extraction steam of a steam turbine which constitutes a combined cycle in combination with the gas turbine is used, so that the steam pressure is usually high. Also, the leakage of steam in the gas turbine must be minimized for the reason of the steam-side cycle. Therefore, in the steam cooling of the stationary blade of gas turbine, the stationary blade is required
(1) to have a pressure resisting strength that withstand the steam pressure, PA1 (2) to have a steam passage open to the outside and to have a supply port and a recovery port, PA1 (3) to have a low thermal stress, and PA1 (4) to be easy in manufacturing. PA1 (1) An inside shroud and an outside shroud are air-cooled. PA1 (2) A trailing edge portion of a blade portion, which is thin in shape, is air-cooled. PA1 (3) In the present invention described in item (2), part of air which has cooled the trailing edge portion of the blade portion is discharged from the side of an inside shroud as inside seal air for a combustion gas passage.
In the conventional stationary blade of gas turbine, as indicated by arrows in FIGS. 3 and 4, cooling steam enters the stationary blade of gas turbine through a cooling steam inlet 32 of an outside shroud 31, and after passing through an impingement plate 39, it goes through an inward cooling passage 34 provided in a blade portion 33, and is turned at an inside shroud 35. After that, the cooling steam passes through an outward cooling passage 36 provided in the blade portion 33, and is recovered at a cooling steam outlet 37.
Besides the aforementioned stationary blade of gas turbine, a stationary blade in which only the inside shroud is air-cooled has been proposed as disclosed in Japanese Patent Application No. 8-749 filed by the applicant of this invention. In Japanese Patent Application No. 8-749, as shown in FIG. 3, in addition to the aforementioned configuration, cooling air is introduced into the inside shroud 35 through a cooling air inlet 40. The cooling air is allowed to flow through the impingement plate 39 to cool the inside shroud 35. After cooling, the air is allowed to flow into a main gas flow F through a film cooling hole 38 provided in the inside shroud 35 to perform film cooling.
The present steam-cooled stationary blade of gas turbine is in the above-described state and certainly advantageous in terms of efficiency. However, its closed, long, and bent passage is complicated in construction, so that it is difficult to manufacture. In addition to this, if the wall thickness is increased to increase the pressure resisting strength, the whole blade becomes rigid, which poses a problem of disadvantage in terms of thermal stress.
The present invention was made to solve the above problems.